You read off the OUTER scale (which goes the opposite way) instead of the INNER scale. The question says one arm lines up with 0° on the INNER scale, so you must read the inner scale at the other arm. The outer scale shows 45° at the same spot, but the correct reading is 135°.
PRIMARY 4 · MATHEMATICS
Angles
Top 5 mistakes
Ranked by how often they appear across 35 MOE-aligned practice questions in our archive.
You computed 180° − 125° or read the outer scale and added 10°. The correct reading is the value on the inner scale where the second arm lands, which is 135°.
You misread the scale by 10°. The arm points to the 135° mark, not 145°. Take care to read the exact line on the protractor, not one tick further.
You used 90° − 55° = 35° instead of 145° − 90°. The 145° angle is the WHOLE that is being split into 90° (pole-to-ground) and the unknown part. So unknown = 145° − 90° = 55°, not 35°.
You may have computed 155° − 90° = 65° (using 155 instead of 145). Reread the question: the total angle is 145°, not 155°. So 145° − 90° = 55°, not 65°.
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